South Korea's recent public acknowledgement of North Korean's defections, including two senior North Korean officials, aims to show the ruling party's achievements in dealing with North Korea, and is also part of its campaign for the upcoming elections, observers said.

The South's Unification and Defense ministries said on Monday a North Korean army colonel defected last year and had been granted political asylum. He had worked in the secretive General Reconnaissance Bureau, which is focused on espionage activities against the South, Reuters reported.

South Korea's Unification Ministry said a senior diplomat who was posted in an African country had defected to the South last year with his family.

South Korea announced on Friday that 13 workers at a restaurant run by the North in an unidentified country had defected, a case it described as unprecedented.

Asked about the workers on Monday, Chinese foreign ministry spokesperson Lu Kang said it had received a report about a group of 13 North Koreans in China who had gone missing and said that they had used valid passports to leave the country normally on April 6.

"These people had valid identity documents and legally came to the country, not North Koreans who have entered illegally," Lu said, adding that North Koreans who illegally enter the country have always been dealt with in accordance with humanitarian principles under domestic and international law.

The high-profile acknowledgement from the South may be intended to hype up Pyongyang's instability, Dong Xiangrong, a research fellow at the Chinese Academy of Social Sciences, told the Global Times.

Lü Chao, a research fellow at the Liaoning Academy of Social Sciences, told the Global Times that relations between Pyongyang and Seoul is a decisive factor in winning Wednesday's parliamentary elections, and the reported defections can be used to highlight the ruling party's achievements.

The main liberal opposition Minjoo Party accused the government of President Park Geun-hye of trying to influence voter turnout ahead of the elections. Both ministries denied suggestions that revelations were made for domestic political reasons and said disclosing the defections was in the public interest, Reuters reported.